source/libs/mpfr/mpfr-3.1.3/src/cache.c

   1 /* mpfr_cache -- cache interface for multiple-precision constants in MPFR.
   2
   3 Copyright 2004-2015 Free Software Foundation, Inc.
   4 Contributed by the AriC and Caramel projects, INRIA.
   5
   6 This file is part of the GNU MPFR Library.
   7
   8 The GNU MPFR Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MPFR Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
  20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
  21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
  22
  23 #include "mpfr-impl.h"
  24
  25 #if 0 /* this function is not used/documented/tested so far, it could be
  26          useful if some user wants to add a new constant to mpfr, and
  27          implement a cache mechanism for that constant */
  28 void
  29 mpfr_init_cache (mpfr_cache_t cache, int (*func)(mpfr_ptr, mpfr_rnd_t))
  30 {
  31   MPFR_PREC (cache->x) = 0; /* Invalid prec to detect that the cache is not
  32                                valid. Maybe add a flag? */
  33   cache->func = func;
  34 }
  35 #endif
  36
  37 void
  38 mpfr_clear_cache (mpfr_cache_t cache)
  39 {
  40   if (MPFR_PREC (cache->x) != 0)
  41     mpfr_clear (cache->x);
  42   MPFR_PREC (cache->x) = 0;
  43 }
  44
  45 int
  46 mpfr_cache (mpfr_ptr dest, mpfr_cache_t cache, mpfr_rnd_t rnd)
  47 {
  48   mpfr_prec_t prec = MPFR_PREC (dest);
  49   mpfr_prec_t pold = MPFR_PREC (cache->x);
  50   int inexact, sign;
  51   MPFR_SAVE_EXPO_DECL (expo);
  52
  53   MPFR_SAVE_EXPO_MARK (expo);
  54
  55   if (MPFR_UNLIKELY (prec > pold))
  56     {
  57       /* No previous result in the cache or the precision of the
  58          previous result is not sufficient. */
  59
  60       if (MPFR_UNLIKELY (pold == 0))  /* No previous result. */
  61         mpfr_init2 (cache->x, prec);
  62
  63       /* Update the cache. */
  64       pold = prec;
  65       /* no need to keep the previous value */
  66       mpfr_set_prec (cache->x, pold);
  67       cache->inexact = (*cache->func) (cache->x, MPFR_RNDN);
  68     }
  69
  70   /* now pold >= prec is the precision of cache->x */
  71
  72   /* First, check if the cache has the exact value (unlikely).
  73      Else the exact value is between (assuming x=cache->x > 0):
  74        x and x+ulp(x) if cache->inexact < 0,
  75        x-ulp(x) and x if cache->inexact > 0,
  76      and abs(x-exact) <= ulp(x)/2. */
  77
  78   /* we assume all cached constants are positive */
  79   MPFR_ASSERTN (MPFR_IS_POS (cache->x)); /* TODO... */
  80   sign = MPFR_SIGN (cache->x);
  81   MPFR_SET_EXP (dest, MPFR_GET_EXP (cache->x));
  82   MPFR_SET_SIGN (dest, sign);
  83
  84   /* round cache->x from precision pold down to precision prec */
  85   MPFR_RNDRAW_GEN (inexact, dest,
  86                    MPFR_MANT (cache->x), pold, rnd, sign,
  87                    if (MPFR_UNLIKELY (cache->inexact == 0))
  88                      {
  89                        if ((_sp[0] & _ulp) == 0)
  90                          {
  91                            inexact = -sign;
  92                            goto trunc_doit;
  93                          }
  94                        else
  95                          goto addoneulp;
  96                      }
  97                    else if (cache->inexact < 0)
  98                      goto addoneulp;
  99                    else /* cache->inexact > 0 */
 100                      {
 101                        inexact = -sign;
 102                        goto trunc_doit;
 103                      },
 104                    if (MPFR_UNLIKELY (++MPFR_EXP (dest) > __gmpfr_emax))
 105                      mpfr_overflow (dest, rnd, sign);
 106                   );
 107
 108   if (MPFR_LIKELY (cache->inexact != 0))
 109     {
 110       switch (rnd)
 111         {
 112         case MPFR_RNDZ:
 113         case MPFR_RNDD:
 114           if (MPFR_UNLIKELY (inexact == 0))
 115             {
 116               inexact = cache->inexact;
 117               if (inexact > 0)
 118                 {
 119                   mpfr_nextbelow (dest);
 120                   inexact = -inexact;
 121                 }
 122             }
 123           break;
 124         case MPFR_RNDU:
 125         case MPFR_RNDA:
 126           if (MPFR_UNLIKELY (inexact == 0))
 127             {
 128               inexact = cache->inexact;
 129               if (inexact < 0)
 130                 {
 131                   mpfr_nextabove (dest);
 132                   inexact = -inexact;
 133                 }
 134             }
 135           break;
 136         default: /* MPFR_RNDN */
 137           if (MPFR_UNLIKELY(inexact == 0))
 138             inexact = cache->inexact;
 139           break;
 140         }
 141     }
 142
 143   MPFR_SAVE_EXPO_FREE (expo);
 144   return mpfr_check_range (dest, inexact, rnd);
 145 }